Field of the Invention
This invention relates to a semiconductor testing circuit and a method of testing a semiconductor circuit.
The present invention has many applications which include, but not be limited to, a liquid crystal display device in which a plurality of video signals are selected to drive pixels.
A known active matrix-type liquid crystal display device (LCD) has a structure shown in FIG. 13, for example. The LCD includes a circuit array substrate, a counter substrate provided opposite to the array substrate with a counter electrode 16, and a liquid crystal layer 15 held between the array substrate and the counter electrode 16. The array substrate is provided with (m.times.n) pixel electrodes 14 disposed in a matrix form, m scanning lines Y1 through Ym provided along the columns of the pixel electrodes 14, n signal lines X1 through Xn, thin film transistors (TFTs) 13 provided in the vicinities of crossing points of the scanning lines Y1 through Ym and the signal lines X1 through Xn a scanning line driver circuit 18 to drive the scanning lines Y1 through Ym, and a signal line driver circuit 19 to drive the signal lines X1 through Xn. Each TFT is used for a switching element which supplies a video signal voltage, when it is turned on, in response to a scanning voltage applied to its corresponding scanning line. The pixel electrode 14 and the counter electrode 16 are made of a transparent and electrically conductive material. The counter electrode 16 is driven by a counter electrode driving circuit 20.
The scanning line driver circuit 18 sequentially supplies the scanning voltage to the scanning lines Y1 through Ym during a horizontal scanning period. The signal line driver circuit 19 supplies the video signal voltage to the signal lines X1 through Xn during the horizontal scanning period. The liquid crystal layer 15 is driven by the difference between the video signal voltage supplied to the pixel electrode 14 and predetermined voltages supplied to the counter electrode 16 from the counter electrode driving circuit 20. The liquid crystal layer 15 passes light beams from the pixel electrode 14 to the counter electrode 16 in accordance with its voltage-optical transmission characteristic.
The signal line driver circuit 19 plays an important role in supplying pixel (video) signals to the pixel electrodes 14 If the signal line driver circuit 19 has malfunctions in its output circuit, it stops furnishing pixel signals to rows of the pixel electrodes 14 corresponding thereto and line defects appear on the screen of the liquid crystal display device. Even if only one line defect exists on the screen, it is fatal to the liquid crystal display device. In order to secure its efficiency and reliability, it should not be shipped unless the output of such a signal line driver circuit has been tested. Further, analysis and assessment of actual defects in liquid crystal display devices are useful for increase of the production yield of products to be manufactured from now on. Thus, it is essential to test an output of a key circuit like the signal line driver circuit.
Further, both signal lines and a signal line driver circuit are made on a glass substrate in a driver circuit integrated-type LCD. In this case, since the degree of integration is quite high and a physical space is hardly left to contact the probes to the output terminals, the testing, itself, becomes quite difficult.
As explained above, it is difficult to test the output of the signal driver circuit in the conventional LCDs though such a test is important to secure the reliability and improve the production yield.